The present invention relates generally to chemical mechanical planarization of semiconductors, and more particularly, to methods and apparatus for conditioning polishing pads used in chemical mechanical planarization.
The concept of applying chemical and mechanical abrasion to a semiconductor substrate is generally known as chemical mechanical planarization or chemical mechanical polishing (xe2x80x9cCMPxe2x80x9d). Typically, CMP involves mounting a semiconductor wafer on a fixture and rotating the wafer face against a polishing pad. The polishing pad is typically mounted on a moving platen, thereby effecting multiple directions of movement between the rotating wafer and the polishing pad. A slurry containing an abrasive and a chemical that chemically interacts with the wafer face is flowed between the wafer and the polishing pad. In integrated circuit wafer fabrication, CMP is commonly applied to planarize dielectric layers, metallization layers, and other wafer layers.
FIG. 1 shows some major components of a typical CMP apparatus. Examples of such apparatuses are known in the art and are available, for example, from SpeedfamIPEC of Chandler, Ariz. The CMP apparatus 100 includes a wafer carrier 128 that is fitted with an air chamber 126 (shown in phantom lines), which is designed to secure a wafer 124 by vacuum to the wafer carrier 128 during wafer loading typically before the CMP is to commence. During CMP, however, the wafer 124 is bound by xe2x80x9cwear ringsxe2x80x9d, not shown, within the wafer carrier 128 such that a wafer surface that is to be polished contacts a polishing pad 102. During CMP, the polishing pad 102 orbits while the wafer 124 rotates.
A conventional polishing pad 102 for use with an apparatus such as illustrated in FIG. 1 includes a plurality of slurry injection holes 120, and adheres to a flexible pad backing 104 which includes a plurality of corresponding pad backing holes 118. A slurry mesh 106, typically in the form of a screen-like structure, is positioned below the pad backing 104. An air bladder 108 capable of inflating or deflating is disposed between a plumbing reservoir 110 and the slurry mesh 106. The air bladder 108 pressurizes to apply the polishing force. A co-axial shaft 112, through which a slurry inlet 114 (shown by phantom lines) is provided to deliver slurry through the plumbing reservoir 110 and the air bladder 108 to the slurry mesh 106, is attached to the bottom of plumbing reservoir 110. Slurry is delivered to the system by an external low pressure pump, and is distributed on the polishing pad surface by centripetal force, the polishing action, and slurry pressure distribution on the pad 102. The polishing pad 102 may also be provided with grooves or perforations (not shown) for slurry distribution and improved pad-wafer contact.
After polishing multiple wafers using the same polishing pad over a period of time, the polishing pad suffers from xe2x80x9cpad glazingxe2x80x9d. As is well known in the art, pad glazing results when particles that have eroded from the wafer surface, along with the abrasives from the slurry, tend to glaze or accumulate over the polishing pad. A glazed layer on the polishing pad typically forms atop the eroded wafer and slurry particles that are embedded in the porosity or fibers of the polishing pad. Pad glazing is particularly pronounced during planarization of an oxide layer such as a silicon dioxide layer (hereinafter referred to as xe2x80x9coxide CMPxe2x80x9d). By way of example, during oxide CMP, eroded silicon dioxide particulate residue accumulates along with abrasive particles from the slurry to form a glaze on the polishing pad. Pad glazing is undesirable because it reduces the polishing rate of the wafer surface and produces a non-uniformly polished wafer surface. The non-uniformity results because glazed layers are often unevenly distributed over a polishing pad surface.
One way of achieving and maintaining a high and stable polishing rate is by conditioning the polishing pad on a regular basis. For example, the polishing pad may be conditioned every time after a wafer has been polished. During pad conditioning, an abrasive conditioning bar or an abrasive disk is typically contacted with the polishing pad, which may be rotating or in an orbital movement.
One type of conditioning operation employs a conditioning bar that swept across the face of rotating polishing pad. The conditioning bar is mounted on a mounting element and includes an abrasive surface. The mounting element imparts pivotal or linear movement to the conditioning bar. The abrasive surface, which often includes diamond particles, operates to condition the polishing pad through the relative motion of the conditioning bar and the polishing pad.
One problem with current conditioning operations is the relatively short life of the conditioning bars. One type of conditioning bar that is commonly used includes a diamond tape or strip that is wrapped over a flexible foam support. The diamond strip may be readily replace as the abrasiveness of the strip degrades. However, the CMP slurry also tends to degrade the flexible foam support. In particular, the harsh chemical environment created by the slurry causes degradation of the flexible foam support, thereby mandating relatively frequent replacement.
An alternative design employs rigid steel bar with diamond grid plates adhered to the steel bar. Among other things, the rigid steel bar design is relatively expensive to manufacture and handle. In particular, providing fixturing features and/or adhering the grid plates requires tooling and processing steps specific to steel. Moreover, the rigid steel bar is not impervious to the slurry chemicals.
Accordingly, a need exists for a CMP polishing pad conditioning bar that avoids or reduces the drawbacks associated with conditioning bars that employ a flexible foam support or a steel support.
The present invention addresses the above stated needs, as well as others, by providing a conditioning bar that uses a polycarbonate support member on which is supported an abrasion member. Preferably, the polycarbonate support member is reinforced by a rigid metal element, with the polycarbonate member disposed at least in part between the abrasion member and the rigid metal element. By employing a polycarbonate support member, the expense associated with a complex shaped and formed steel conditioning bar is avoided. Even if a rigid metal element reinforcement is employed, the metal reinforcement element need only be a simple bar or rod, which is relatively inexpensive to form. Moreover, the exposure of the metal reinforcement to slurry chemicals is limited by the polycarbonate member, thereby reducing possibility for degradation.
A first embodiment of the invention is a conditioning bar assembly that includes a polycarbonate member, an abrasion member, and a rigid metal element. The abrasion member is supported on an outer surface of the polycarbonate member. The rigid metal element is supported on the polycarbonate member, at least a portion of the polycarbonate member disposed between the rigid metal element and at least a portion of the abrasion member.
Another embodiment of the invention is a conditioning bar assembly that includes an elongate polycarbonate member and an abrasion member. The elongate polycarbonate member is constructed of an inert plastic material. The abrasion member is removably supported on at least one side of the elongate polycarbonate member. Preferably, the abrasion member is an abrasive tape, but may also include abrasive grid plates.